1. Field of the Invention
The present invention relates to a belt for a continuously variable transmission, which comprises a metal ring assembly comprising a plurality of endless metal rings laminated one on another, and a large number of metal elements each having a ring slot into which the metal ring assembly is fitted, the belt being wound around a drive pulley and a driven pulley, so that pulley-abutment faces of the metal elements abut against V-faces of the drive pulley and the driven pulley, thereby transmitting a driving force between both the pulleys.
2. Description of the Related Art
There is a metal belt for a continuously variable transmission which is known from Japanese Patent application Laid-open No.7-12177, and which is designed so that the excessive rolling of metal elements can be inhibited, whereby the metal elements can be smoothly meshed with pulleys, by setting tanxe2x88x921B/A at a value lower than 1xc2x0, wherein A represents a distance between an outer end of one of left and right saddles faces of a metal element and an inner end of a lower face of an ear on the side opposite from the saddle face, and B represents a distance between a radially outer peripheral surface of a metal ring assembly and the lower face of the ear.
The groove width of a ring slot in the metal element is set slightly larger than the thickness of the metal ring assembly fitted in the ring slot. In the metal ring assembly supported at its radially inner peripheral surface on a saddle face of the ring slot, a small clearance is defined between the radially inner peripheral surface and the lower face of the ear. Therefore, a rolling of the metal elements relative to the metal ring assembly is permitted to an extent where the radially outer peripheral surface of the metal ring assembly is not brought into contact with the lower faces of the ear of the metal element. However, when the maximum rolling angle (which is defined herein as a limit rolling angle) of the metal elements within a range that the radially outer peripheral surface of the metal ring assembly does not interfere with the lower face of the ear is too large, namely, the clearance between the metal ring assembly and the lower face of the ear is large, and when the limit rolling angle is too small, there is a problem that the power transmitting efficiency of the metal belt decreases.
The present invention has been accomplished with the above circumstance in view, and it is an object of the present invention to ensure that the power transmitting efficiency of the metal belt is maintained at a high value and the durability of the metal ring assembly is enhanced by defining the range of the limit rolling angle of the metal elements.
To achieve the above object, according to a first feature of the present invention, there is provided a belt for a continuously variable transmission, which comprises a metal ring assembly formed of a plurality of endless metal rings laminated one on another, and a large number of metal elements each having a ring slot into which the metal ring assembly is fitted, the belt being wound around a drive pulley and a driven pulley in such a manner that pulley-abutment faces of the metal elements abut against V-faces of the drive pulley and the driven pulley for transmitting a driving force between both of the pulleys, wherein the relationship between the thickness of the metal ring assembly and the groove width of the ring slot is established so that a limit rolling angle xcex1 defined as a rolling angle of the metal elements provided when a radially outer peripheral surface of the metal ring assembly contacts a radially outer edge of the ring slot in the metal element is in a range of 0.7xc2x0 less than xcex1 less than 2.5xc2x0.
According to a second feature of the present invention, the upper limit value of the limit rolling angle xcex1 of the metal elements is set as a value of a rolling angle at which the power transmitting efficiency of the belt is equal to or larger than a predetermined value.
According to a third feature of the present invention, the lower limit value of the limit rolling angle xcex1 of the metal elements is set as a value of a rolling angle generated following the deformation of the V-face due to an axial thrust on the drive pulley or the driven pulley.
With the above features, the relationship between the thickness of the metal ring assembly and the groove width of the ring slot is established so that the limit rolling angle xcex1 of the metal elements is smaller than 2.5xc2x0. Therefore, it is possible to prevent the metal elements from being moved disorderly due to a large limit rolling angle xcex1 equal to or larger than 2.5xc2x0 which causes a pinching between the metal elements and the V-faces of the pulley, thereby preventing a reduction in power transmitting efficiency. In addition, the relationship between the thickness of the metal ring assembly and the groove width of the ring slot is established so that the limit rolling angle xcex1 of the metal elements exceeds 0.7xc2x0. Therefore, when the metal elements are forcibly rolled with the deformation of the V-faces due to the axial thrust on the pulley, such rolling can be prevented from being inhibited by the interference between the metal ring assembly and the lower faces of the ear with each other, thereby preventing the pinching between the metal elements and the V-faces of the pulley. Therefore, it is possible to prevent a decrease in power transmitting efficiency and a decrease in durability of the metal ring assembly.